Method for the production of hard fiberboards



METHOD FOR THE PRODUCTION OF HARD FIBERBOARDS Hermann Basler, Munich, Germany No Drawing. Application September 11, 1951, Serial No. 246,176

Claims priority, application Germany March 23, 1949 3 Claims. (CI. 92-61) This invention relates to the production of hard fiber boards and particularly wear-resistant boards to be used for building purposes as well as floor boards, wall boards and the like; it is a continuation-in-part of my pending U. S. patent application Ser. No. 96,161 filed May 28, 1949, now abandoned.

For the manufacture of these hard fiber boards, a fiber pulp is produced by disintegration and particularly grinding of wooden bodies and particles, for instance in steel disc mills, or by the extrusion of wood fibers at a high pressure from nozzles, whereby an explosion-like expansion and defibration of the wood components results.

The wood fibers are by the admixture of binders, such as phenol aldehyde resins, by the removal of water, by shaping procedures and by heat compression converted into the final boards.

This manufacture is often initiated in machines provided with longitudinal screens or in casting presses and completed by heat-compression of the produced fiber cakes in hydraulic presses. The thus produced hard plates or boards, of which the hardness mainly depends upon the percentage of hardening resins, are then ready for use. The hardness and particularly the surface hardness may be additionally varied by the application of lacquers or artificial resins to the outer face of the articles.

Another type of hard fiber boards is produced by compressing wood chips, wood flour and similar small-sized vegetable matter upon admixture of binders, such as hardening resins or coated wood chips, coated wood flour and coated other small-sized vegetable matter at a high pressure of, for instance, 200 kilograms per square centimeter.

If greater quantities of resinous binders are used, these methods assume a great similarity to the methods of pressing mixtures of artificial resins into plates with its inherent disadvantage of an uneven distribution of the materials, which are charged into the press; this drawback of uneven distribution of the materials charged into the press molds is even more apparent, when the quantity of the added resins is reduced, the flow of the heated material in the press being hereby greatly diminished and the fibers prematurely enveloped and glued together by the resins which quickly harden at the high pressing temperature; in this manner not only an unequal thickness results of the plates and a poor surface configuration, but this procedure is partly incomplete, because due to the uneven accumulation of the charged materials unequal pressure conditions result, which lead to injuries and even breakage of the presses. In spite of greatest care being taken to effect an even distribution of the charge unequal strength of the final boards cannot be avoided. This method therefore has been greater drawbacks than the first described process.

Many attempts have been made to manufacture building boards directly from wood; the inferior properties of these boards are generally known; they dry easily, tear and warp.

, In order to eliminate the deficiencies of these wood made boards, plywood boards were created. The manufacture of plywood boards is extremely expensive and practically unusable for ordinary building: purposes.

Moreover, it is also known to use small-sized wooden pieces and to combine the same into boards by pressure and heat. This process has never attained practical usefulness, as it is impossible to sufiiciently uniformly arrange these wooden pieces in order to exert upon the same a uniform pressure action; the wooden pieces remain bulky and unwieldy and do not combine into a uniform mass; the boards and plates made from these small wooden bodies and admixtures therefore have different mechanical qualities, and particularly a different pressure resistance and hardness; moreover, the thus produced boards are inclined to warp.

The great drawback of all the above referred to manufacturing procedures consists therein that boards of a uniform structure and uniform wear could not be produced from wood and from products which are derived from the working of wood, such as particularly chips, and pulp or fines.

It is the main object of the invention to produce from these physically divergent materials a hard fiber board and particularly a large size fiber board, which possesses an astounding uniformity of its mechanical and chemical properties, therefore may be successfully used as a first class structural and building element and particularly wall and floor board.

The combined use of wood chips and wood pulp for the production of boards, is, of course, known as such; however, by the instant particular pretreatment of the chips and their combination with the fiber pulp the grave disadvantages of the art, and particularly the hitherto typical non-uniformity of the final board is eliminated.

The conversion of the mixture of chips and of fiber pulp, which latter contains a large percentage of up to 98% water into a board is often performed on a grate by the combined action of suction and jolting and in the presence of binders.

It is also true that the pulp tends to create a uniform, distribution of the chips and fill out the cavities there-v between. However, that type of uniformity, which is adapted to create equal mechanical properties of the final boards and particularly equal stress resistance which is so greatly needed in hard boards for building and similar purposes, is not attainable by the hitherto known hard board manufacturing processes.

It is one of the main objects of the invention to fill,

this gap and to enable, from mixtures of fiber and pulp, the production of hard boards, of a hitherto unattained structure equality.

It is a further object of the invention to produce a hard board for building and constructional purposes which possesses uniform stress resistance and bearing properties.

The attainment of these remarkable objects of hard boards made of mixtures of fiber pulp and chips is based on the recognition that during the compression of the latter a surprisingly large number of hardly noticeable cavi ties are formed between the mixture components due to the irregular and unwieldy shape of the chips. These cavities are not filled with the pulp particles during the compression of the. boards and they cause the non-uniform structure and therewith mechanical properies of the final boards.

In order to remedy this grave disadvantage, which has heretofore escaped the knowledge in the art, the chips are plasticized prior to their admixture with the pulp.

This plastieizing action may be achieved by treating the chips with a diluted alkaline solution or by boiling the same or subjecting them to any other treatment, whereby the chips are softened and made ductile and their unyielding character is eliminated.

The creation of cavities ordinarily caused by the unyielding character and irregular shape of the chips is prevented because the softened ductile chips fill the cavities between the pulp particles and a hard board results which excels in uniform mechanical properties and particularly stress resistance.

Independently of the mixture ratio of the chips and the pulp it is advisible, that the total quantity of solids in the final aqueous mixture should not be more than 25 per cent and preferably only 1-2 per cent.

The binding capacity of the uniform pulp and chip mixture within the final boards is increased to such a degree that it is possible to grind the boards to a thickness of 1 millimeter or less without a reduction of their cohesion and resistive capacity.

As stated above, diluted alkali solutions are foremostly adapted for the plasticizing treatment of the chips; however, any other method to render the chips ductile, such as a treatment in hot or boiling water, answers the requirement of this invention. Therefore, the term plasticizing used in the claims defines a treatment of the chips whereby their unyielding and unwieldy properties are eliminated and they are softened and converted into a ductile state, whereby the elasticity of the chips increases without destroying their texture.

Upon admixture of the plasticized chips with the fiber pulp and exposure to pressure, a practically uniform body results as the fines easily penetrate into and fill any, even the smallest cavity of the flexible chips; this entrance of the fines into the spaces between the non-treated chips would have been prevented by their stiffness and insufiicient bendability. The chemical pretreatment of the chips and similar wooden bodies enables the production of a single layer board of which the mechanical qualities, such as particularly resistance, bendability, elasticity are superior to the hitherto customary multi-layer boards, of which the inner layers generally consist of chip and pulp mixtures and the outer layers of chips only. The enormous economical advantages of the one layer board of the invention over a multi-layer board is clearly apparent; however, the mechanical properties of the instant single layer board are greatly superior to those of the multi-layer type for the reasons set forth, as this specification proceeds.

The invention will now be described more in detail.

Example 1 100 kilograms wood chips having a length of about 10 millimeters and a thickness of preferably not more than one millimeter are exposed in a closed vessel to a pressure treatment with steam of about 1 atm. for about 1 to 2 hours.

The chips are now submitted to a plasticizing treatment preferably at an elevated temperature of between 40-80 C.

For this purpose, they are stirred into a diluted aqueous alkali, for instance NaOH solution, containing about 1 per cent of an emulsion of bitumen, paraifin or the like high melting hydrocarbons. Approximately an 8 per cent resin dispersion or emulsion is preferably added. Upon uniform distribution and mixture, the mass is brought to a pH equal to 45 by the admixture of an acid.

100 kilograms chips are defibrated into a pulp in the customary manner. This pulp is subjected to an aftertreatment in a beater-or refiner to produce a fiber pulp mixture containing at least 5 per cent slimes.

The chips are mixed with this aqueous fiber pulp and in'such a manner that the percentage of solids is about 98 per cent; hereupon the mixture is dewatered in the usual 4 manner in a Fourdrinier or long sieve machine to form the board.

A proportion of the plasticized chips relative to the fines should be between about 40-70 per cent. A board is preformed from this mixture in the usual manner and then finally treated in a closed hot press for the removal of the water; binders may be added, if desired.

Instead of admixing the plasticized chips to the pulp, a mixture may be made of the untreated chips and the pulp and the mixture may be subjected to the described plasticizing treatment.

Example 2 The wood chips are dried in a heated chamber to a residual moisture content of not more than 1 per cent.

The chips are dipped into a paraffin emulsion, which may be replaced or to which may be added a solution of an artificial resin or of linseed oil, which penetrates well into the porous structure of the chips. At the same time dyes may be added.

The thus treated chips are treated as described in Example 1 with the exception that the admixture of the bitumen or paraffin dispersions or emulsions is omitted.

Example 3 Mixtures of chips and fiber pulp are preliminarily compressed into boards at a pressure of up to 8 kilograms.

The thus pre-compressed boards are impregnated with the solution or suspension of one of the above described plasticizers. Hereupon, the thus treated board is finally compressed at a temperature of above 140 C.

Example 4 The chip and fiber pulp mixtures produced in conformity with the foregoing examples are compressed in a hotpress at a pressure of only about 8 kilograms and at a temperature which lies beneath the condensation point of the added materials. The thus prepressed boards are surface-impregnated with a spray of artificial lacquers or drying oils; they are hereafter finally compressed at a temperature above 140 C.

Example 5 The boards are surfaced with lacquers which harden at a normal temperature, for instance cellulose lacquers, at a ratio of about 100 grams per square meter of the board surface.

Since certain changes in carrying out the above process could be made without departing from the scope thereof, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows.

1. A method for the manufacture of hard fiber board comprising mixing about 40 to 70 parts by weight of steam treated wood chips of a thickness less than about 1 millimeter with 60 to parts by weight of aqueous cellulose fiber pulp, treating said mixture with a dilute aqueous sodium hydroxide solution containing about 1% of paraffin emulsion at a temperature of about -80 C. to plasticise said mixture, acidifying said mixture, dewatering said mixture to form a plasticized mixture of chips and pulp in the form of a sheet and pressing said sheet while heating to a temperature above 140 C. to form a hard board.

2. A method as claimed in claim 1 wherein said aqueous cellulose fiber pulp contains at least 5% slimes.

3. A method for the manufacture of hard fiber board comprising mixing about 40 to 70 parts by weight of steam treated wood chips of a thickness less than about 1 millimeter with to 30 parts by weight of aqueous cellulose fiber pulp, said wood chips being plasticized with a dilute aqueous sodium hydroxide solution contain- 6 ing about 1% of paraffin emulsion at a temperature of 1,995,145 Frost Mar. 19, 1935 about 40-8() and being acidified, dewatering said mix- 2,026,765 Woodford Jan. 7, 1936 ture to form a plasticized mixture of chips and pulp in 2,080,077 Howard et a1. ..1 May 11, 1937 the form of a sheet and pressing said sheet while heat- 2,098,733 Sale Nov. 9, 1937 ing to a temperature above 140 C. to form a hard board. 5 2,131,097 Drewsen Sept. 27, 1938 2,143,840 Buchanan et a1. Jan. 17, 1939 References Cited in the file of this patent 2,319,267 Sawyer May 18, 1943 2,338,602 Schur Ian. 4, 1944 UNITED STATES PATENTS 2,402,160 Heritage June 18, 1946 45,510 Ff 201 1864 10 2,441,169 Roman May 11, 1948 514,027 P11111198 1894 2,44 ,304 Roman 3, 194 806,954 Colahan 12, 1905 2,538,742 Willey Jan. 16, 1951 858,411 McFarland July 2, 1907 1,500,208 Shaw July 8, 1924 FOREIGN PATENTS 1,511,475 Howell Oct. 14, 1924 15 3,294 Holland June 2, 1919 1,672,988 Novak June 12, 1928 309,211 Great Britain Apr. 8, 1929 1,748,832 Duhaml Feb. 25, 1930 1,818,039 Busch Aug. 11, 1931 OTHER REFERENCES 1,857,432 Codwise May 10, 1932 Tennet: Paper Industry and Paper World, December 1,875,075 Mason Aug. 30, 1932 20 1945, pages 1357-1358 (Copy in Sci. Lib.) 1,894,577 Wells Jan. 17, 1933 

1. A METHOD FOR THE MANUFACTURE OF HARD FIBER BOARD COMPRISING MIXING ABOUT 40 TO 70 PARTS BY WEIGHT OF STEAM TREATED WOOD CHIPS OF A THICKNESS LESS THAN ABOUT 1 MILLIMETER WITH 60 TO 30 PARTS BY WEIGHT OF AQUEOUS CELLULOSE FIBER PULP, TREATING SAID MIXTURE WITH A DILUTE AQUEOUS SODIUM HYDROXIDE SOLUTION CONTAINING ABOUT 1% OF PARAFFIN EMULSION AT A TEMPERATURE OF ABOUT 40-80* C. TO PLASTICISE SAID MIXTURE, ACIDIFYING SAID MIXTURE, DEWATERING SAID MIXTURE TO FORM A PLASTICIZED MIXTURE OF CHIPS AND PULP IN THE FORM OF A SHEET AND PRESSING SAID SHEET WHILE HEATING TO A TEMPERATURE ABOVE 140* C. TO FORM A HARD BOARD. 